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United States Patent |
5,075,764
|
Yamazaki
|
December 24, 1991
|
Diamond electric device and manufacturing method for the same
Abstract
An electric device such as a light emitting device utilizing a diamond film
is described. The diamond film is partially doped with an impurity
selected from Group IIb or VIb of the periodic table. The doping is
performed with a patterned semiconductor film as a mask in a self-aligning
manner. An electrode arrangement is formed on the semiconductor film or
the doped diamond film so that stability of contacts can be obtained.
Inventors:
|
Yamazaki; Shunpei (Tokyo, JP)
|
Assignee:
|
Semiconductor Energy Laboratory Co., Ltd. (Kanagawa, JP)
|
Appl. No.:
|
537991 |
Filed:
|
June 13, 1990 |
Foreign Application Priority Data
| Jun 22, 1989[JP] | 1-159867 |
| Jun 26, 1989[JP] | 1-162997 |
Current U.S. Class: |
257/752; 257/760; 257/E29.082; 257/E33.015; 257/E33.017; 257/E33.06; 257/E33.065; 438/47; 438/105 |
Intern'l Class: |
H01L 023/48; H01L 029/46; H01L 029/54; H01L 029/62 |
Field of Search: |
357/71,80
437/209
|
References Cited
U.S. Patent Documents
4764804 | Aug., 1988 | Sahara et al. | 437/209.
|
Foreign Patent Documents |
59-213126 | Dec., 1984 | JP.
| |
60-246627 | Dec., 1985 | JP.
| |
61-263141 | Nov., 1986 | JP.
| |
Primary Examiner: James; Andrew J.
Assistant Examiner: Davenport; T.
Attorney, Agent or Firm: Sixbey, Friedman, Leedom & Ferguson
Claims
What is claimed is:
1. A diamond electric device comprising:
a semiconductor substrate;
a diamond formed on said semiconductor substrate;
a semiconductor film formed on a portion of said diamond film; and
an electrode formed on said semiconductor film;
wherein an impurity is selectively added into a region of said diamond
except for said portion on which said semiconductor film and electrode
have been formed.
2. The electric device of claim 1, wherein the semiconductor substrate
comprises a p or n-type silicon semiconductor while the semiconductor film
comprises a silicon containing semiconductor having a conductivity type
opposite to that of the substrate.
3. The electric device of claim 2 wherein the semiconductor film comprises
silicon carbide.
4. The electric device of claim 1 wherein said impurity is an element
selected from the group consisting of Zn, Cd, O, S, Se and Te.
5. The electric device of claim 1 wherein said device is a light emitting
device.
6. The electric device of claim 5 wherein a light emitting region
corresponds to the region of the diamond where the impurity is added.
7. The electric device of claim 1 wherein said electrode is patterned in
the form of a number of parallel strips which are separated from each
adjacent strip.
8. The electric device of claim 7 wherein the impurity doped region is
formed between said strips.
9. The electric device of claim 8 wherein a surface of the impurity doped
region is covered with a silicon carbide film.
10. The electric device of claim 1 further comprising a lower electrode
coated on the rear surface of said substrate opposed to the upper surface
on which said diamond, said semiconductor film and said electrode are
formed.
11. The electric device of claim 1 further comprising an anti-reflection
film formed on said substrate over said diamond, said semiconductor film
and said electrode.
12. The electric device of claim 11 wherein said antireflection film is
made from silicon nitride.
13. A diamond electric device comprising:
an insulating substrate;
a diamond film formed on said substrate; and
at least one electrode formed on said diamond film,
wherein said electrode is electrically connected with said diamond film
through an intervening semiconductor film.
14. The electric device of claim 13 wherein said semiconductor film
comprises a silicon semiconductor.
15. The electric device of claim 13 wherein said semiconductor film
comprises a silicon carbide semiconductor.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to diamond electric devices, more
particularly to diamond semiconductor electric devices such as light
emitting devices, and manufacturing methods for the same.
2. Description of the Prior Art
For emission of reddish light rays, GaAs semiconductors have been utilized
to manufacture light emitting devices for more than a decade. The emission
of blue or green light, as well as white light, however, has long been
hardly realized by means of solid state devices.
The inventor has before proposed to make a light emitting device from
diamond which can emit light at short wavelengths, for example, as
described in Japanese Patent Application No. sho 56-146,930 filed on Sep.
17, 1981. Diamond is promising, as a light emitting substance for mass
production, because of its high thermal resistance, chemical stability and
low price, in view of a great demand for light emitting devices in the
market. It is, however, very difficult to manufacture diamond light
emitting devices at a high yield required for commercialization because
there are formed a large proportion of products whose efficiencies are
undesirably low to satisfy the requirement of the application thereof.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an electric device with
a diamond film having a high performance.
It is another object of the present invention to provide a diamond electric
device having a long life time.
Additional objects, advantages and novel features of the present invention
will be set forth in the description which follows, and in part will
become apparent to those skilled in the art upon examination of the
following or may be learned by practice of the present invention. The
object and advantages of the invention may be realized and attained by
means of the instrumentalities and combinations particularly pointed out
in the appended claims.
The present invention has been culminated based upon the discovery of the
origin of the low yield of diamond light emitting device manufacture. The
light emitting action of diamond light emitting devices takes place when a
relatively large current is passed through diamond crystals by applying a
voltage between a pair of electrodes sandwiching the diamond crystals. The
electric energy carried by the current, however, is consumed largely only
to produce heat rather than to emit light rays. The inventor succeeded in
the discovery of the origin of the low efficiencies and the heat
generation. As a result, it has been found that schottokey contacts
between diamond films and metal electrodes can not be formed with stable
characteristics and desired performance. Diamond films hardly make good
electrical contact with metal surfaces. Futhermore, it is very difficult
to deposit a diamond film having an n-type conductivity while the
formation of p-type diamond films is relatively easy.
In order to accomplish the foregoing and other objects and advantages, it
is proposed to add an impurity to a diamond film with which a metallic
electrode makes contact. The doping of an impurity makes it possible to
form a satisfactory contact between diamond and a metal and increases the
conductivity of the diamond film so that current tends to flow
preferentially through the impurity diamond. In a preferred embodiment,
the doping to the diamond film is only partially effected. If an electrode
is formed on the undoped portion, a usual semiconductor film such as a
silicon semiconductor film, which are relatively easy to make suitable
contact with the electrode, is interposed between the electrode and the
diamond film. The direct contact between undoped diamond and a metal is
avoided in this structure.
By this structure, metallic electrodes make electrical contact only with
impurity diamond or usual semiconductor films and therefore
metal-semiconductor contacts can be easily formed without dispersed
characteristics. One of the important applications is in the diamond light
emitting device. The current passing through the diamond film induces
recombination of electron-hole pairs between mid-gap states (radiation
centers), between the mid-gap states and a valence band, between a
conduction band and the mid-gap states and between the conduction band and
the valence band. The spectrum of light emitted from a diamond film is
determined by differential energy levels between the mid-gap states, the
bottom of the conduction band and the apex of the valence band. Depending
upon the differential levels, it is possible to emit blue or green light
or radiation having a continuous spectrum of wavelengths over a relatively
wide range such as white light. For example when a dopant of an element of
Group IIa such as zinc or cadmium or an element of Group VIb such as
oxygen, sulfer, selenium or tellurium is introduced, e.g. by ion
implantation, effective radiation of blue light can be observed. The
associated intervening semiconductor films are doped with an element of
Group IIIb such as boron, aluminum, gallium or indium, or an element of
Group Vb such as nitrogn, arsenic or antimony in order to form p-type or
n-type semiconductors to make good contact with a metallic electrode.
These elements may be introduced also into the diamond film. The spectra
of radiation, however, tends to shift from a blue region to a green region
in that case.
Ion implantation is suitable for use in formation of such diamond light
emitting devices. The introduction of an impurity can be accomplished in a
uniform manner irrespective of diverse geometries of diamond particles and
morphology of crystalline structure. The ion bombardment produces many
defects in the diamond films. The defects can function as recombination
centers from which light emission occurs. If the addition of an impurity
is carried out only by diffusion, the impurity is concentrated at grain
boundaries and the activity of the diamond film is substantially reduced.
Preferably, after the ion implantation, the diamond film is subjected to
thermal annealing in air or an oxidizing atmosphere such as oxygen or NOx
atmosphere at 200.degree. to 1000.degree. C., e.g. 800.degree. C. By this
treatment, only atomic level distortion is alleviated leaving defects, and
therefore the number of recombination centers is not reduced. What is more
advantageous is the fact that the ion implantation into the diamond film
decreases the resistivity of the impurity diamond film so that current
tends to flow selectively through the implanted diamond.
The structure of light emitting devices and impurities suitable to form
diamond films capable of emitting blue light are described infra in
accordance with a preferred embodiment of the present invention.
A diamond film containing an element of Group IIb of the periodic table is
deposited on an insulating substrate, for example, by plasma vapor
reaction of a reactive gas comprising (CH.sub.3).sub.2 Zn and CH.sub.3 OH
diluted with hydrogen. An n-type semiconductor film is deposited as a
buffer film on the diamond film. The semiconductor film is partially
removed, and an element of Group VIb or IIb (VIb preferred) such as S or
Se is selectively added to the exposed diamond film. On the semiconductor
film or the exposed diamond film, a pair of electrodes are formed through
a buffer film if necessary.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and form a part of the
invention and, together with the description, serve to explain the
principles of the invention.
FIG. 1 is a cross sectional view showing a CVD apparatus for use in forming
diamond light emitting devices in accordance with the present invention.
FIGS. 2(A) to 2(D) are cross sectional views showing a method of
manufacturing diamond light emitting devices in accordance with a first
embodiment of the present invention.
FIGS. 3(A) to 3(D) are cross sectional views showing a method of
manufacturing diamond light emitting devices in accordance with a second
embodiment of the present invention.
FIGS. 4(A) to 4(D) are cross sectional views showing a method of
manufacturing diamond light emitting devices in accordance with a fourth
embodiment of the present invention.
FIGS. 5 and 6 are cross sectional views showing diamond light emitting
devices in accordance with fifth and sixth embodiments of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The formation of diamond films by means of chemical vapor reaction has been
proposed by the applicant in Japanese Patent Application No. sho 61-292859
filed on Dec. 9th, 1986 and U.S. patent application Ser. No. 07/178,362.
Hereinbelow, the process of the formation of diamond are discussed.
Referring now to FIG. 1, a microwave-assisted CVD apparatus provided with
associated Helmholtz coils 17 and 17' for use in depositing diamond films
is shown. The apparatus comprises a vacuum chamber defining a deposition
space 19 therein, a microwave generator 18 connected to the chamber
through an attenuator 16 and a quartz window 45, a gas introduction system
having four inlet ports 21 to 24, a gas evacuation system 25 coupled with
the chamber through a pressure controlling valve and a substrate holder 13
provided in the chamber and with a substrate position adjusting mechanism
42 for supporting a substrate 1 at an appropriate position. By the use of
the adjusting mechanism 42, the axial position of the holder can be
adjusted in order to change the volume of the reactive spece 19. The
evacuation system funtions both as a pressure controller and as a stop
valve. The pressure in the chamber is adjusted by means of the valve. The
inside of the chamber and the holder 13 are circular and coaxial with each
other. The procedure for depositing diamond films in the apparatus is as
follow.
The substrate, for example, a single crystalline silicon semiconductor
wafer of 2 to 6 inches, e.g. 4 inches diameter, is mounted on the holder
13. The surface of the substrate is preferably given scratches in advance
which form focuses for crystalline growth. The scratches are formed for
example by putting the substrate in a liquid in which diamond fine
particles are dispersed and applying ultrasonic waves thereto for 1 minute
to 1 hour. After fixing the substrate 1 on the holder 13 with a keeper 14,
the pressure in the reaction space 19 is reduced to 10.sup.-3 to 10.sup.-8
Torr by means of the evacuation system followed by introduction of a
reactive gas to a pressure of 0.01 to 3 Torr, typically 0.1 to 1 Torr,
e.g. 0.26 Torr. The reactive gas comprises --OH bonds, e.g. an alcohol
such as methyl alcohol (CH.sub.3 OH) or ethyl alcohol (C.sub.2 H.sub.5 OH)
diluted with hydrogen at a volume ratio of alcohol/hydrogen=0.4 to 2. The
hydrogen is introduced through the port 22 at 100 SCCM and the alcohol
through the port 21 at 70 SCCM for example. The coils are energized during
the deposition to induce a magnetic field having a maximum strength of 2K
Gauss and a resonating strength of 875 Gauss at the surface of the
substrate 1 to be coated. Then, microwaves are applied at 1 to 5 GHz, e.g.
2.45 GHz up to 10 KW in the direction parallel to the direction of the
magnetic field to cause ionized particles of the reactive gas in the form
of plasma to resonate therewith in the magnetic field. As a result, a
polycrystalline film of diamond grows on the substrate. A 2 hour
deposition for example can form a diamond film of 0.5 to 5 micrometers
thickness, e.g. 1.3 micrometers thickness. During the deposition of
diamond film, carbon graphite is also deposited. However, the graphite,
which is relatively chemically unstable as compared with diamond, reacts
with radicals which also occur in the plasma of the alcohol and is removed
from the deposited film. The temperature of the substrate 1 is elevated to
200.degree. C. to 1000.degree. C., typically 300.degree. C. to 900.degree.
C., e.g. 800.degree. C. by microwaves. If the substrate temperature is too
elevated, water cooling is effected to the substrate holder 13. If the
substrate temperature is too low, the substrate is heated from the holder
side by means of a heating means (not shown).
In accordance with prefered embodiments of the present invention, some
impurities may be introduced into diamond films during deposition.
Examples of such impurities include S, Se and Te. In case of S, H.sub.2 S
or (CH.sub.3).sub.2 S may be introduced as a dopant together with the
reactive gas at a volume ratio of dopant gas/alcohol=0.001 to 0.03. In the
same manner, H.sub.2 Se, H.sub.2 Te, (CH.sub.3).sub.2 Se and
(CH.sub.3).sub.2 Te can be used as dopant gases. Also, elements of Group
IIb such as Zn and Cd can be introduced using a dopant gas of hydrogen or
organic compound thereof. For example, Zn(CH.sub.3).sub.2 is used as a
dopant gas and introduced together with CH.sub.3 OH at a volume ratio of
Zn(CH.sub.3).sub.2 /CH.sub.3 OH=0.005 to 0.03. If p-type diamond is
desired, methyl boron may be input together with alcohol, e.g. at a volume
ratio of B(CH.sub.3).sub.3 /CH.sub.3 OH=0.005 to 0.03.
Referring now to FIGS. 2(A) to 2(D), a method of forming a light emitting
device in accordance with a first embodiment of the present invention will
be explained. A diamond coating 2 is deposited on a p-type silicon
semiconductor substrate 1 of a 4-inch wafer to a thickness of 0.5 to 3.0
micrometers, e.g. 1.3 micrometers, by the microwave-assisted plasma CVD
method in a magnetic field as described above. The surface of the
substrate 1 to be coated has been given scratches. During the deposition,
Zn(CH.sub.3).sub.2 or B(CH.sub.3).sub.3 is introduced, if desired, as a
dopant gas together with CH.sub.3 OH diluted by hydrogen at a volume ratio
of CH.sub.3 OH/H.sub.2 =0.8. The volume ratio of the dopant gas/CH.sub.3
OH is 0.005 to 0.03.
An n-type semiconductor film 3 of silicon or a silicon carbide (SixC.sub.1
-x; 0<.times.<1, pref. 0<.times.<0.5) is deposited on the diamond film 2
to a thickness of 300 angstroms to 0.3 micro-meter in the same manner as
the diamond film except that silane, in place of the alcohol, is used
together with a dopant gas of PH.sub.4. In the case of silicon carbide, a
carbon compound gas such as CH.sub.4 is further introduced. On the
semiconductor film 2, a metallic film of molybdenum or tungstem is further
deposited to a thickness of 0.1 to 0.5 micrometer. Such a refractory metal
film is suitable in view of the following thermal annealing procedure. If
the temperature throughout the manufacturing process is not elevated above
500.degree. C., an aluminum film is deposited instead to a thickness of
0.5 to 2 micrometers.
The metallic film 12 is coated with a suitable photoresist mask and
patterned by dry etching to form electrodes 12-1, 12-2, . . . , 12-n in
the form of strips or a comb. The underlying semiconductor film 3 is also
patterned following the dry etching of the electrodes in a self-aligning
manner to leave semiconductor regions 3-1, 3-2, . . . , 3-n corresponding
to the electrodes 12-1, . . . 12-n. The exposed portions of the underlying
diamond film 2 is then doped with S or Se with the electrodes as a mask by
applying an acceleration voltage of 50 to 200 KeV to a density of
1.times.10.sup.18 to 3.times.10.sup.20 cm.sup.-3, e.g. 2.times.10.sup.19
cm.sup.-3. The diamond film 2 is subjected to thermal annealing in an
oxygen atmosphere or in air to introduce oxygen into the ion doped regions
5-1 to 5-n of the diamond film 2. As a result, a PIN junction is formed
between the substrate 1 and the semiconductor film 3. A lead 8 is attached
to the electrode by a known wire bonding technique. The upper surface of
the structure is coated with a silicon nitride film 6 for the purpose of
antireflection as shown in FIG. 2(D). The bottom surface of the substrate
1 is coated with a lower electrode 9. Finally, the structure is enclosed
by a transparent plastic moulding in order to obtain mechanical strength
and a wet-proof structure.
In this structure, current flows from the substrate 1 to the electrodes
12-1, . . . 12-n through the substrate 1, the diamond film 2, the ion
doped regions 5-1 to 5-n and the silicon semiconductor film 3-1, 3-2, . .
. , 3-n in this order. Light emission takes place mainly in the ion doped
regions of the diamond film 2 and for this reason light rays can emit
outward without no impediment of the silicon semiconductor film 6. When a
voltage of 10 to 200 V (e.g. 50 V) was applied across the diamond film 2
of the diamond light emitting device between the upper electrode 12 and
the lower electrode 9, the diamond emitted blue visual light (475 nm.+-.5
nm) at 14 cd/m.sup.2 by virtue of current passing therethrough. The
voltage may be applied as a DC voltage or as a pulse train at no higher
than 100 Hz of a duty ratio of 50%. The light emission was not reduced
even after continuing operation for a month.
A second embodiment will be described in below in conjunction with FIGS.
3(A) to 3(D) which are very similar as FIGS. 2(A) to 2(D) and therefore
the manufacturing process is largely similar as the first embodiment
except for those particularly described in the followings. Corresponding
explanations will be dispensed with.
A diamond film 2 of 0.5 to 3 micrometers average thickness is deposited on
an n-type silicon semiconductor substrate 1. The diamond film is not doped
with any impurity. A p-type silicon carbide semiconductor film 3 and an
upper molybdenum or tungstem film 12 are deposited on the diamond film 2.
These films 3 and 12 are covered with a mask 4 in the same manner as the
first embodiment. The following photo-etching is effected only partially
and not completely through the silicon carbide film 3. Bottom portion of
the semiconductor film 3 contacting the diamond film 2 is left even after
the etching as shown by 15-1 to 15-n.
Next, as illustrated in FIG. 1(C), zinc (Group IIb) is introduced into the
diamond film 2 by ion implantation to 9.5.times.10.sup.19 cm.sup.-3 to
form impurity regions 5-1, 5-2, . . . 5-n. This silicon carbide regions 32
effectively function as a protector of the ion implanted diamond film 2.
The optical energy gap of the silicon carbide is desirably controlled to
be no lower than 2.5 eV in order not to form impediment to radiation from
the diamond film 2.
In this embodiment, the structure is formed with an N-diamond-P junction
which is reverse to the P-diamond-N junction of the first embodiment. An
element of Group IIb instead of Group VIb is used as impurity functioning
as radiation centers. On the diamond film which is not doped, the impurity
semiconductor film is located as a buffer film and a current path. The
semiconductor film and the overlying electrode arrangement are patterned
into a number of parallel strips with the light emitting doped diamond
regions 5-1, . . . 5-n therebetween. When a 40 V was applied between the
electrode 7 and the substrate 1, 11 cd/cm.sup.2 light emission at 480 nm
(blue) was observed. The illumination is darker as compared to that of the
first embodiment. However, it is sufficient for commercialization.
A third embodiment will be described in below. This embodiment can be
illustrated also in conjunction with FIGS. 2(A) to 2(D) like the first
embodiment and therefore the manufacturing process is largely similar as
the first embodiment except for those particularly described in the
followings. No redundant description will not repeated.
In this embodiment, a diamond film 2 is deposited using a boron dopant to
be a p-type diamond film on a p-type silicon semiconductor substrate 1. An
n-type silicon carbide film 3 is formed on the diamond film 2. Upper
electrodes 12-1, . . . 12-n are formed on the film 3 in the same manner as
the first embodiment. Then, Se (Group VIb) is introduced into the diamond
film 2 by ion implantation at an accelation voltage of 50 to 200 KeV to
1.times.10.sup.19 to 3.times.10.sup.20 cm.sup.-3 to form impurity regions
5-2, 5-2, . . . 5-n followed by thermal annealing in air to also introduce
oxygen into the impurity regions. Accordingly, two elements of Group VIb
(oxygen and selenium) are added to the diamond film. This embodiment is
excellent in long-term stability. The emission was 22 cd/m.sup.2 at 510
nm, which was greenish blue.
Referring now to FIGS. 4(A) to 4(D), a method of forming a light emitting
device in accordance with a fourth embodiment of the present invention
will be explained. A substrate 31 having an insulated surface is prepared
by coating a silicon semiconductor substrate 31-1 with a silicon nitride
film 31-2 of 0.1 to 0.5 micrometer thickness. The surface of the substrate
31 to be coated is given scratches. A diamond coating 32 is deposited on
the substrate 31 to a thickness of 0.5 to 3 micrometers by the
microwave-assisted plasma CVD method in a magnetic field as described
above. Zn(CH.sub.3).sub.2 or B(CH.sub.3).sub.3 is introduced, if desired,
during the deposition as dopant gas together with CH.sub.3 OH diluted by
hydrogen at a volume ratio of CH.sub.3 OH/H.sub.2 =0.8. The volume ratio
of dopant gas/CH.sub.3 OH is 0.005 to 0.03.
On the diamond film 32, a p-type semiconductor film 33 of silicon or a
silicon carbide (SixC.sub.1 -x; 0<x<1, preferably 0<x<0.5) is deposited to
a thickness of 300 angstroms to 0.3 micrometer in the same manner as the
diamond film except that silane (SiH.sub.4) is used together with a dopant
gas of B.sub.2 H.sub.6 in place of the alcohol. In the case of silicon
carbide, a carbon compound gas such as CH.sub.4 is further introduced. The
semiconductor film 3 is coated with a suitable photoresist mask 34 and
patterned to leave buffer films 33 and 33'. The exposed portions of the
underlying diamond film 32 is then doped with S or Se with the mask over
the buffer films 3 by an accelation voltage of 50 to 200 KeV to a density
of 1.times.10.sup.18 to 5.times.10.sup.20 cm.sup.-3, e.g.
6.times.10.sup.19 cm.sup.-3. By this procedure, the boundary of the doped
region 35 (impurity diamond) of the diamond film 32 is coincident with the
perimeter of the mask 34, i.e. the perimeter of the buffer films 3, and
therefore dispersion of characteristics, such as the standard voltage to
be applied thereto, of products can be minimized. The substrate 31 is then
subjected to thermal treatment in an oxygen atmosphere or air to introduce
oxygen into the ion doped regions 35-1 to 35-n. After the thermal
treatment, silicon oxide occuring on the surface of the buffer films 33
and 33' is removed by putting the substrate 31 in a thin hydrofluoric
acid. Then, a 0.05 to 0.5 micrometer thick molybdenum or tungstem film and
a 0.5 to 2 micrometers thick aluminum film are deposited on the structure
over the semiconductor film 33. These metallic films are selectively
removed by photoetching through another photoresist mask in order to form
electrodes 39-1, 39-2, 59-1 and 59-2. The molybdenum or tungstem electrode
39-1 and 39-2 functions also as a buffer film. The aluminum electrodes
39-2 and 59-2 are provided for making electrical contact with leads 38 and
58 which are attached by a known wire bonding technique. The upper surface
of the structure is coated with an antireflection film of silicon nitride
6 and enclosed with a transparent plastic moulding in the same manner as
the previous embodiments.
In this structure, current laterally flows from the electrodes 39-1 and
39-2 (or another electrically connected electrode 39-1' and 39-2') to the
electrodes 59-1 and 59-2 through the undoped diamond 32 and the ion doped
diamond film 35 in that order. Light emission takes place mainly in the
ion doped regions of the diamond film 32 and for this reason light rays
can emit outward without no impediment of the silicon semiconductor film
32 and the silicon carbide film 32. When a voltage of 10 to 200 V (e.g. 50
V) was applied between the leads 38 and 58, diamond emitted blue visual
light (475 nm.+-.5 nm) at 17 cd/m.sup.2 by virtue of current passing
through the ion implanted diamond.
A fifth embodiment will be described hereinbelow in conjunction with FIG.
5. The manufacturing process is largely similar as the fourth embodiment
except for those particularly described in the followings and therefore no
redundant explanation will be repeated.
A diamond film 32 of 0.5 to 3 micrometers average thickness is deposited on
an insulating substrate 31. The diamond film 32 is not doped with any
impurity. A p-type silicon or silicon carbide semiconductor film is
deposited on the diamond film 32. The semiconductor film is covered with a
mask and patterned to form buffer films 33 and 33' in the same manner as
the fourth embodiment.
Next, zinc (Group IIb) is introduced into the diamond film 32 by ion
implantation to 9.5.times.10.sup.19 cm.sup.-3 to form impurity regions 55
with the mask and the buffer films 33 and 33'. An aluminum film of 1.5
micrometers thickness is deposited and patterned with another mask (not
shown) to form electrodes 39, 39' and 49 followed by thermal annealing at
400.degree. to 500.degree. C. in air. The thermal annealing is carried out
at temperatures no higher than 500.degree. C. in an oxidizing atromsphere
in general. In this embodiment, the electrode 49 is in direct contact with
the diamond film, which is doped with an impurity. When a 40 V was applied
between the electrodes 39, 39' and 49, 14 cd/cm.sup.2 light emission at
480 nm was obserbed. The illumination is darker than that of the fourth
embodiment. However, it is sufficient for commercialization.
A sixth embodiment will be described in conjunction with FIG. 6. The
manufacturing process is largely similar as the fourth embodiment except
for those particularly described in the followings and therefore similar
explanation will be omitted.
In this embodiment, a diamond film 32 is deposited on an insulated
semiconductor wafer 31 using a dopant of oxygen. An n-type silicon carbide
film is formed on the diamond film 2 and patterned to leave buffer films
33, 33' and 33" in the form of a number of teeth of a comb for
constructing a large light emitting area. Then, Se (Group VIb) is
introduced into the diamond film 2 by ion implantation at an accelaration
voltage of 50 to 200 KeV to 1.times.10.sup.19 to 6.times.10.sup.20
cm.sup.-3 to form impurity regions 5-1, 5-2, . . . 5-n followed by thermal
annealing in air to further introduce oxygen into the impurity regions.
Accordingly, two elements of Group VIb are added to the diamond film.
Other buffer films 49-1 and 49-2 of a p-type semiconductor are formed on
the doped regions 55. Silicon oxide formed at the surface of the
semiconductor film 33, 33', 33", 49-1 and 49-1' is removed by a thin
hydrofluoric acid. Then, aluminum electrodes 39, 39', 39", 49-2 and 49-2'
are formed on the semiconductor films. After dicing the wafer into a
number of such light emitting devices, each device is mounted on a lead
frame or a stem structure followed by wire bonding of lead wiring 38 and
58. This embodiment is excellent in long-term stability. The emission was
29 cd/m.sup.2 at 490.+-.10 nm, which was greenish blue.
As described above, in accordance with the embodiments of the present
invention, diamond devices can be manufactured only with one or two
photomasks and a very high yeild is expected. For example, nearly 10000
light emitting elements of 0.8 mm.times.0.8 mm can be formed within the
4-inch wafer.
The foregoing description of preferred embodiments has been presented for
purposes of illustration and description. It is not intended to be
exhaustive or to limit the invention to the precise form described, and
obviously many modifications and variations are possible in light of the
above teaching. The embodiment was chosen in order to explain most clearly
the principles of the invention and its practical application thereby to
enable others in the art to utilize most effectively the invention in
various embodiments and with various modifications as are suited to the
particular use comtemplated. For example, diamond electric device in
accordance with the present invention can be manufactured in a
multichamber apparatus comprising a first chamber for deposition of p-type
semiconductors, a second chamber for deposition of diamond and a third
chamber of deposition of n-type semiconductors. These chambers are coupled
in series in order to streamline the deposition. The patterns of the
electrodes and the semiconductor film are also not limited to those
described above, coaxial circles or other configurations can be employed
in order to comply with the requirement of the application thereof.
The present invention is broadly applicable to any electric device
comprising a diamond film. These electric devices can be formed on a
single substrate, i.e. and integrated circuit device which may consists of
diamond light emitting devices, diamond diodes, diamond transistors,
diamond resistances, diamond capacitors and the like. Of course, it is
possible to severe a single substrate, after a number of diamond devices
are formed on the substrate, into individual separate devices.
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